A honeycomb structure made of a ceramic material (hereinafter referred to as the ceramic honeycomb structure) is broadly used as a catalyst substrate, various types of filters, an adsorber, an absorber and the like. As to this ceramic honeycomb structure, in recent years, with the stricter regulation on an exhaust gas, various attempts to improve a purification performance have been made.
For example, in the ceramic honeycomb structure used as a catalyst substrate for an oxide catalyst system or three way catalyst system in which harmful substances in the exhaust gas discharged from a car, such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide (NOx) are purified, attempts to improve the catalyst activity at an early stage are made by reducing the thicknesses of partition walls to decrease a heat capacity, and then rapidly raising the temperature of a catalyst immediately after the engine starting. Moreover, attempts to exert a desired exhaust gas purification performance immediately are made by increasing the number of cells to large contact area between the exhaust gas and the catalyst. Furthermore, attempts to improve the catalyst activity are also made by increasing the porosities of the partition walls to decrease the heat capacity. Studies on the combinations of the thicknesses and porosities of the partition walls have been actively conducted. Incidentally, it is to be noted that examples of prior art documents include Patent Documents 1, 2.
[Patent Document 1] JP-A-H7-39760
[Patent Document 2] JP-A-2007-021483